Digital-to-shaft position information translator



D. SIGEL June 2, 1959 DIGITAL-TO-SHAFT POSITION INFORMATION' TRANSLAT'ORFiled June l, 1956 2 Sheets-Sheet 1 umm Nwwuunm @QQ Nm Nom HI l|l RH WNYmm ZM D. SIGEL June 2, 1959 DIGITAL-TO-SHAT POSITION INFORMATIONTRANSLATOR Filed June 1, 1956 2 Sheets-Sheet 2 INVENTOR ATTORNEY swam.:f om@ www United States Patent O DIGITAL- O-SHAFT POSITION INFORMATIONTRANSLATOR David Sigel, Bayonne, NJ., assignor to InternationalTelephone and Telegraph Corporation, Nutley, NJ., a corporation ofMaryland Application June 1, 1956, Serial No. 588,917

4 Claims. (Cl. S18- 28) This invention relates in general to a shaftpositioning apparatus and in particular to a positioning device whichresponds to digital information and translates this information into anangular indication.

It is often desirable to convert digital information which is usually ina binary coded form into an angular position either for direct readingpurposes or as used in digital-to-analog computer translations. Thereare variout methods known to the art for accomplishing this result. Apopular method is to use a plurality of servos with combinations of theservos representing the digital bits. Another method is the use of camswith each cam representing the weight of the binary code bits beingused, coupled with a relay control and mechanical detenting operation.These various methods accomplish the translation of digital informationto shaft position information with varying degrees of yspeed and varyingdegress of component requirements.

An object of this invention is to convert electrical signalsrepresenting digital information to a shaft position with a combinationof resistances and hence with an economy of components while notsacrificing speed or accuracy. v

One of the features of this invention is the provision of electricallyvariable taps on an endless potentiometer. By`disposing the tapselectrically through switches which are controlled by the digitalinformation, the potentiometer wiper will seek the proper quadrant ofthe po tentiometer and subsequently the proper point to' balance thebridge thereby eliminating any possibility of ambiguity which mightoccur without the variable taps.

A second feature of the invention is the provision of switches used inconjunction with the voltage divider to short out portions of thevoltage divider and thereby effectively move the tap on the voltagedivider in accordance with the digital information while physically atap remains stationary.

The above-mentioned and other features and objects of this inventionwill become more apparent by reference to the following descriptiontaken in conjunction with the accompanying drawings, in Which:

Fig. l is a block diagram of the apparatus;

Figs. 2A, 2B, 2C and 2D are illustrations of the various tap positionsfor various readings;

Fig. 3 is a schematic diagram of the tap switching circuit; and

Fig. 4 is a schematic diagram showing the voltage divider circuit.

As shown in Fig. l, digital information is received at point 1 andconditions the relays represented by block 2. Certain relays areenergized While others are deenergized to represent a coded number. Therelay points act as switches which when used in conjunction with voltagedivider 3, short out certain portions of the divider thus effectivelymoving the tap up and down the divider. Other relay points at 4 serve asswitches to change the tap combinations of points 5, 6, 7 and 8depending on what is the correct selection of taps. The

2,889,505 Patented June 2K, 1959 output of voltage divider 3 isconnected to and alcts as one leg of the bridge circuit 9. Depending onthe position of shaft 10, the potentiometer wiper 11 determines apotential value. This potential value is also connected to andrepresents the other leg of the resistor bridge 9. An unbalance of theresistor bridge is directed to the servo amplier 12, and in turn to themotor 13 which drives the shaft 10 until the wiper 11 reaches a point ofbalancewhen compared with the output of voltage di'- vider 3.

Illustrations 2A, 2B, 2C and l2D represent the taps which are applicablein order for the wiper 11 to find a point of no ambiguity and at thesame time a correct indication. The selection of the taps as shown isaccomplished by the switches at 4 of Fig. 1 and is set up as soon as thedigital information conditions the relays.

In Fig. 3 the circuitry represented in box 4 of Fig. l 1s disclosed.Fig. 3 is shown connecting the taps at 135 degrees and 315 degrees withthe positive and negative reference potential points. The arrangement ofthe relay straps and points at 14, 15, 16 and 17 would be effected whendigital information such as represented in Fig. 2A was available tocondition the relays 18 and 19. To further illustrate: if digitalinformation which should be represented by an indication on the circularpotentiometer between and including 180 to 269, which would be acondition as `shown by Fig. 2C, is presented, then relay 18 would beattracted and relay straps 16 and 17 would transfer to effect a plusterminal at 135 and a ground terminal 'at 315. The circuitry of thevoltage divider is shown in Fig. 4. The switches operate in pairs asshown by the numbers and their corresponding primed numbers. As thepoints of 20 are closed the points of 20' are opened andnlikewise as anynon-primed switch is closed, its primed counterpart is opened. Theresistances have Weighted values depending on the code being used. Aweighted 1, 2, 4 and 8 code is shown by way of illustration. By changingand adding resistances as described above, tap 21 is effectively movedup and down the voltage divider. `The overall resistance value shown inFig. 4 by adding l22, 23 and 24 is one half the total of the circularpotentiometer hence the taps 5, 6, 7 and 8 as shown in Fig.` 1 on thecircular potentiometer are arranged in combination to place a potentialon each half of the potentiometer. The total resistance of Fig. 4 lessthe resistance 22 and 24 (the variable resistance part of the voltagedivider) represents only one fourth the resistance value of the circularpotentiometer so there is a need of our combinations of taps torepresent a full circle.k Other resistance and potentiometer relationscould be set up depending on the need but the quadrant arrangement isshown here by way of illustration. To eliminate ambiguity of shaftposition the principle of the slope of the potential is relied on.Assuming a condition where taps 7 and S of Fig. 1 are energized with thepositive tap at point 7, then at first it would seem to be possible forthe wiper 11 to 'be in two positions where a balanced potential couldexist with only one position being correct. If the wiper 11 reached apoint between zero degrees and degrees, this would be the correctposition according to the scheme shown in Fig. 2A. However, it canreadily be seen that a point of the same balance potential is foundbetween degrees and 315 degrees following the potential gradientclockwise but this point would be incorrect since the potential at point7 would be made positive only if the digital information receivedindicated that the angle 6 which represents this digital information wasbetween zero and 90 degrees. Making a second assumption that if there isan unbalance of bridge 9 and it indicates a lesser potential value onthe potentiometer than on the voltage divider the shaft will be drivencounter clockwise and vice Versa for a greater potential value of thepotentiometer, the prevention of ambiguity becomes apparent. If thewiper were at 230 degrees and this point represented a greater potentialthan the voltage divider potential, the motor would drive the shaftclockwise and as the wiper traveled toward the tap 7, an even greaterpotential would be experienced by the wiper. Under my second assumptionthe greater potential would keep the motor driving clockwise, and hencethe wiper would drive beyond tap 7 causing the wiper to travel along thepotentiometer until it reached the correct potential between zero and 90degrees. If the wiper passed beyond the correct point while traveling inthis clockwise direction the potential of the endless potentiometer asexperienced by the wiper would become less than the voltage divider andthis would cause the motor to reverse, moving the wiper to the correctposition. If originally when my wiper was sitting at 230 degrees, thispoint had been a lesser potential than the voltage divider the motorwould have been driven counterclockise according to my secondassumption. As the wiper moved counterclockwise along the endlesspotentiometer, the potential experienced-by the wiper would be of even alesser value than the voltage divider as the wiper moved toward tap 5.The motor would continue to drive the shaft and the wipercounterclockwise to the quadrant between zero and 90 degrees until thewiper experienced the correct balanced potential, and in a fashionsimilar to that described above, if the Wiper-were overdriven thepotential on the endless potentiometer would experience a greater valueand reverse the motor. Hence there can be no ambiguity and the digitalinformation received can be represented by only one position of theshaft.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

I claim:

1. A digital-to-shaft position information translator apparatuscomprising a source of coded digital information, a motor, a shaftcoupled to said motor and Whose position is solely and directlycontrolled by said motor, an endless potentiometer with a plurality oftaps and a wiper coupled for movement with said shaft, a voltage dividercircuit, first means coupled to said plurality of taps and responsive tothe coded information to be represented by the position of said shaft,to apply a potential to a selected pair of said taps without changingthe position of said shaft, said selected pair of taps effecting apotential gradient along the entire endless potentiometer simultaneouslyclockwise and counterclockwise from the first of said taps to the secondof said taps, second means responsive to the input coded informationcoupled to said voltage divider circuit to vary the output therefrom, abridge circuit, first circuitry means coupling the respective outputs ofsaid potentiometer and said voltage divider circuit to said bridgecircuit, and second circuitry means coupling the output of said bridgecircuit to said motor to drive said shaft in accordance with anyunbalance present in said bridge circuit.

2. A digital-to-shaft position information translator apparatuscomprising a source of coded digital information, a motor, a shaftcoupled to said motor and whose position is solely and directlycontrolled by said motor, an endless potentiometer with a plurality oftaps and a wiper coupled for movement with said shaft, a voltage dividercircuit, a plurality of relays having associated relay points coupled tosaid plurality of taps and responsive to the received coded information,reference potential means coupled to said relays to apply therethrough apotential to a selected pair of said taps without changing the positionof said shaft, said selected pair of taps effecting a potential gradientalong the entire endless potentiometer simultaneously clockwise andcounterclockwise from the rst of said taps to the second of said taps,second means responsive to the input coded information coupled to saidvoltage divider circuit to vary the output therefrom, a bridge circuit,first circuitry means coupling the respective outputs of saidpotentiometer and said voltage divider circuit to said bridge circuit,and second circuitry means coupling the output of said bridge circuit tosaid motor to drive said shaft in accordance with any unbalance presentin said bridge circuit.

3. A digital-to-shaft position information translator apparatuscomprising a source of coded digital information, 'a motor, shaftcoupled to said motor and whose position is solely and directlycontrolled by said motor, an endless potentiometer with a plurality oftaps and a wiper coupled for movement with said shaft, a voltage dividercircuit, rst means coupled to said plurality of taps and responsive tothe coded information to be represented by the position of said shaft toapply a potential to a selected pair of said taps without changing theposition of said shaft, said selected pair of taps effecting a potentialgradient along the entire endless potentiometer simultaneously clockwiseand counterclockwise from the first of said taps to the second of saidtaps, a plurality of relays responsive to the input coded informationwhose points serve as switches to vary the output of said voltagedivider circuit, a bridge circuit, first circuitry means coupling therespective outputs of said potentiometer and said voltage dividercircuit to said bridge circuit, and second circuitry means coupling theoutput of said bridge circuit to said motorl to drive said shaft inaccordance with any unbalance in said bridge.

4. A digital-to-shaft information translator apparatus comprising asource of coded digital information, a motor, a shaft coupled to saidmotor and whose position is solely and directly controlled by saidmotor, an endless potentiometer with a plurality of taps'and a wipercoupled for movement with said shaft, a voltage divider circuit, aplurality of first relays having associated relay points coupled to saidplurality of taps and responsive to the received coded information,reference potential means coupled to said first relay points to applytherethrough a potential to a selected pair of said taps withoutchanging the position of said shaft, said selected pair of tapseffecting a potential gradient along the entire endless potentiometersimultaneously clockwise and counterclockwise from the rst of said tapsto the second of said taps, a plurality of second relays responsive tothe input coded information whose points serve as switches to vary theoutput of said voltage divider circuit, a bridge circuit, lirstcircuitry means coupling the respective outputs of said potentiometerand said voltage divider circuit to said bridge circuit, and secondcircuitry means coupling the output of said bridge circuit to said motorto drive said shaft in accordance with any unbalance present in saidbridge.

References Cited in the le of this patent UNrTED STATES PATENTS

